For Druid/Rogue, there is the Daggerspell Shaper from Complete Adventurer. It allows you to carry the bonuses from the daggers you wield, over to wildshape. So if I had a +1 flaming dagger, and a +2 holy dagger and wildshaped into a lion. The lion's claw attacks would have +1 flaming, and +2 holy on them respectively.

in the same book there's a feat called Savage Grapple, worth checking out for Druid/Rogues

A Barbarian/Druid might do well with the Nature's Warrior PrC, from Complete Warrior. It's for Druids who focus their abilities on fighting while Wild Shaped. Not a bad class at all, but I've always felt it a little risky for pure Druids.

A Rogue/Druid might look into the Black Flame Zealot. The only problem is he/she would need a non-metal Kukri (perhaps irownwood). Otherwise, it's a great class. =) One of my personal favorites for Cleric/Rogues.

According to the DMG (pg 144) Stone weapons have a -2 penalty on attack and damage rolls, which is somewhat arguable.

Then again, a magical stone weapon with a +1 bonus would reduce that to a -1, but still. =P Basically what they're trying to say is that stone weapons suck, at least in comparrison to steel. (Which is easily changed, with, say a harder stone material than simple "stone".)

If your Druid/Rogue or Druid/Barbarian has gotten wildshape, Warshifter from Complete Warrior.

By far, one of the most broken prestige classes made.

(At level 2, while shifted, +4 Str/Con, Immune to crits/sneak attack, and with a standard action, increase the size of your natural weapons by one category.

Really, this class is totally broken for Changlings and Shifters from Eberron, but for Druids it still isn't bad. My favorite build is still the Warshifter/Bear Warrior/Barbarian with Wild on their weapons and armor)

I've actually really liked the idea of a Druidic assassin--someone who wildshapes into a bird or something, flies into someone's room while they're sleeping, slits their throat, then flies out again. I've been designing a Fochlucan Lyricist character (someone already mentioned that PrC) which would do something like that. The FL PrC won't help you want (it's for druid/bard multiclasses, but requires some levels of rogue for some odd reason), but a Druid/Assassin (say, druid 7 /rogue 3/assassin 10 over 20 levels) could be really interesting.